This invention relates to thin film transistors (hereinafter termed "TFTs") and to large area electronic devices (for example electroluminescent displays, plasma displays, electrostatic print heads, and X-ray dynamic beam attenuators) comprising such TFTs.
For many years there has been much interest in developing thin film circuits with TFTs on glass and/or on other inexpensive insulating substrates, for large area electronics applications. Such TFTs fabricated with amorphous or polycrystalline semiconductor films are commonly used to form the switching devices in active matrix liquid crystal displays.
One problem encountered with TFTs is that their use is limited to relatively low power applications, primarily as a result of the low mobility in the deposited semiconductor layer, in comparison to single-crystal ion implanted transistor structures. There is therefore a need to produce a TFT which can be used in higher power applications, for example as switching devices in electroluminescent display panels, plasma display panels or electrostatic printheads.
JP 61-131481A discloses a thin film transistor in which an annular source electrode is disposed concentrically around a central drain pad, to define a channel between the source and drain. This structure reduces the overall size of the transistor to achieve given response characteristics.